Scottish, for someone from "the land of the lochs", referring to Norway.
Gaelic versions are Lachlann, Lachann and the earlier version Lochlain. Laughlan is also likely to be a Gaelic form, influenced by Irish spelling.
A correspondent [RF] has reported a Lachlan whose name was recorded variously as Loctschen, Lewisham, Leoachlean, Leachbean and Leochlean on different documents during his lifetime. Although they are not known to be common, we have included these spellings because they may not be found by Soundex search.